Asymmetric Vlan Core Technology Research

With the popularity of the enterprise Intranet and the rapid development of the Internet, the problems about sharing of enterprise resource and scarcity of VLAN resource were needed to be sloved, so the asymmetric VLAN technology came into being.By analyzing existing asymmetric VLAN technology first, this paper pointed out H3C's existing patented technology (Chinese patent:200510130007.6,200910077501.9) shortcomings:copying the MAC address one-way or two-way, this would lead to waste of FDB entries resource and forwarding efficiency decline. Thus eliminating the MAC address copy and improving the search efficiency of MAC address was the basic principles to design new asymmetric VLAN, this article was based on this principle to design and implement the asymmetric VLAN.Through the analysis of packet forwarding process in asymmetric VLAN, the law between the VLAN number in packet and in MAC address item was found, and the concept of VLAN checksum was put forward. Using the perfect hash to organize and search the VLAN checksum, by calculating the first hash parameter factor, choosing 10 set of parmeter was more reasonable, and also the average generation time and average memory usage of VLAN checksum was caculated, this provided reference data for achieving the VLAN checksum in engineering. Then the VLAN checksum was applied to the packet forwarding process in asymmetric VLAN, avoiding MAC address copy and reducing the total number of MAC address item, through the theoretical calculation, the average search times in VLAN checksum module was less than the double copy model, and close to the one copy model, then the experiments about MAC address search performance also verified that conclusion. At last, by using the asymmetric VLAN simulation platform, the experiments verified the conclusion that the average delay time in VLAN checksum model was better than the double copy model.